The present invention relates to an original feeding apparatus for sequentially feeding an original to an image reading platen of an image reading apparatus such as a copier, facsimile, or scanner. The present invention also relates to an image reading apparatus provided with the original feeding apparatus.
An image reading apparatus such as a copier, facsimile, or scanner sequentially reads an original placed on a platen using a solid state imaging device such as a CCD. An original feeding apparatus is provided for separating originals stacked on a feeder tray into a single sheet and feeding them sequentially to a platen.
Conventionally, in such an original feeding apparatus, a separating device is formed of a pair of rollers rotating in forward and reverse directions, or a roller and a friction pad, and separates originals stacked on a feeder tray into a single sheet. A transport device (such as rollers or a belt) with a register roller is arranged in a feeding path for feeding the original to a platen. A feeding device such as a kick roller is disposed above the feeder tray for kicking out the uppermost sheet to a separating roller (separating device). The feeding device is raised and lowered between a kicking position where the feeding device contacts the uppermost original on the tray (a kicking position) and a retracted position where the feeding device is away from the kicking position.
When the separating device separates the original, the feeding device contacts and kicks out the uppermost sheet on the tray. After the separating device separates the original, when the transport device such as a register roller feeds the original toward the platen, the feeding device retracts away from the sheet to reduce a load on the sheet. Therefore, the kick roller is repeatedly raised and lowered in up and down directions between the retracted position above the feeder tray and the kicking position for each cycle of feeding the original.
In view of efficiency of a reading process, the originals on the tray are fed consecutively to the platen at a predetermined interval. In other words, while one original is read at the platen, the next original is fed from the feeder tray. Japanese Patent Publication (Kokai) No. 2002-179266 discloses a conventional feeding apparatus including a kick roller, a separating roller, a register roller, and a transport roller arranged in this order from the feeder tray to the platen. A motor capable of both forward and reverse rotations lowers the kick roller from a retracted position to a kicking position through a forward drive, and simultaneously drives the kick roller and the separating roller to separate the uppermost sheet on the tray to feed the sheet to the register roller. The motor raises the kick roller to the retracted position with a reverse drive, and simultaneously drives the register roller to separate the originals into a single sheet and then feed the uppermost sheet toward the platen. The single motor is provided for raising and lowering the kick roller in the up and down directions with the forward and reverse rotations, thereby making the structure simple.
In the conventional apparatus, when the drive device such as a motor and solenoid raises and lowers the kick roller in the up and down directions or the kick roller lowers under its own weight, the kick roller always strikes the sheets stacked on a feeder tray with a constant speed. Accordingly, when the kick roller is lowered to the sheet feeder tray (from the retracted position to the kick position), an impact and sound of the striking are repeated. In order to reduce the impact and sound generated when the kick roller strikes the sheet, it is possible to lower the kick roller to the sheet surface gently at a slower speed, or to reduce a speed of the kick roller just prior to the striking.
When the kick roller is lowered at a slower speed, it takes long time to feed the sheet, thereby lowering efficiency of the reading process. When a speed of the kick roller is reduced just prior to the striking, it is difficult to reduce a stroke for raising and lowering the kick roller between the retracted position and the kicking positions. Accordingly, it is difficult to make the apparatus compact. As a result, it is necessary to lower the kick roller arranged above the sheet feeder tray at a constant speed to the kicking position where the kick roller touches the surface of the sheet.
An image reading apparatus such as a scanner reads various types of originals in a color mode, black-and-white mode, or gray scale mode. It has been required to read the originals at a high resolution such as 600 dpi and 1200 dpi. It has been also required to read the originals at a higher speed. Accordingly, it is preferable to consecutively feed sheets stacked on a feeder tray to a platen with a short interval at a speed according to a reading mode. In the color mode, three line sensors of R, G, and B arranged separately read a moving original. In this case, if the original is fed unevenly, or a small impact (or vibration) is applied to an apparatus, a read image becomes blurred. Accordingly, it is difficult to read an image with high reproducibility at a high resolution without blurring or distortion of an image.
In an image reading apparatus having such a feeding mechanism, when an original is fed from a feeder tray at a high speed, it is difficult to read the original at a high resolution in the color mode without blurring or distortion of an image. When the original is fed at a low speed, it is difficult to increase reading efficiency and processing efficiency, especially in the black-and-white mode or at a low resolution.
It has been found that the color blurring and distortion of an image in the color mode or at a high resolution are related to an operation of feeding a next original from a feeder tray. In particular, when a kick roller is lowered and collides with the feeder tray, an impact generates a vibration, which becomes a major factor of the problems.
FIG. 12 shows experimental results showing that the image blurring occurs when a kick roller strikes an original on a feeder tray. In the experiment, the kick roller collided with an upper surface of the original at various speeds from 100 mm/sec to 360 mm/sec. Three sheets of chart paper with a weight of 52.3 grams were placed on the feeder tray. When a second original is kicked out, a shift of an image on a first original was measured. The horizontal axis represents time and the vertical axis represents a percentage of the shift of the image relative to lines with 0.4 mm spacing of the chart paper. A symbol X represents a point when the kick roller collided with the original.
It is clear from the results that the reading platen vibrated by a magnitude substantially proportional to a speed of the kick roller colliding with the originals on the feeder tray. The vibrations moved the original on the platen upwardly and downwardly, thereby causing the blurring and the distortion of image on the original. When a feeding device is lowered to contact an original on a feeder tray at a different speed according to an image reading mode for sequentially feeding the original from the feeder tray to a reading platen, it is possible to reduce the blurring and the distortion of an image.
In view of the problems described above, an object of the present invention is to provide an original feeding apparatus for sequentially feeding an original to an image reading platen at a speed according to a reading mode. Accordingly, it is possible to obtain an image with high quality colors at a high resolution.
Another object of the present invention is to provide an image reading apparatus provided with such an original feeding apparatus.
Further objects and advantages of the invention will be apparent from the following description of the invention.